![\"garegga_fix1\"](\"https:\/\/blog.system11.org\/wp-content\/uploads\/2015\/08\/garegga_fix1.jpg\")
<\/a><\/p>\nThat’s how they look when it happens, it varies a bit but it’s a common theme of square blocks of corruption or the game may boot with sound errors.\u00a0 It looks pretty dramatic, in fact I thought my PCB was broken the day I received mine having not seen the fault before.\u00a0 I checked the 5v and it was perfect, and eventually I checked on another cab and the game came to life with no drama at all.\u00a0 Here’s the problem:<\/p>\n
Now before I show you how to fix this, lets explain why the above part is a problem.\u00a0 The small 8 pin chip MB3771 is a voltage monitor, it’s the job of the voltage monitor to release the RESET line when the power supply has come up to operating voltage.\u00a0 Here’s the Fujitsu datasheet for the part in case you’re curious.<\/p>\n MB3771<\/a><\/p>\n There are three important pieces of information in there, one is the voltage at which the 3771 will reset the game, 4.2v.\u00a0 The second is the function explanation variable Tpo, and the third important part is their example reset circuit:<\/p>\n Unfortunately, Raizing chose to stick a standard 0.1uf decoupling capacitor in there just like all the others on the board.\u00a0 That is 100th of the required value, providing zero delay at all and causing the game to try to boot at 4.2v.\u00a0 Now if you have a power supply that comes up to speed very quickly, you don’t have a problem.\u00a0 If the power comes up a little more slowly you do have a problem, and you end up with a crashed CPU.\u00a0 The reason switch flicking sometimes works is that the PSU caps haven’t completely drained and it appears to fire up more quickly.<\/p>\n So basically, its either a design flaw or a factory assembly mistake – but the end result is the same and all you need to do to fix it, is put a proper cap in there – I used tantalum 10uf\/16v beads.\u00a0 Sorry for the picture focus, but here’s the Japanese Garegga with the new cap fitted:<\/p>\n Note that all the small caps actually look like resistors on this type.\u00a0 Personally I hate them.\u00a0 Make sure you fit the tantalum the right way around – the positive pin goes to pin 1 on the MB3771, the negative goes to ground.\u00a0 Other variants of the board use more traditional 104 caps, here’s the fixed Chinese board:<\/p>\n<\/a><\/p>\n<\/a>See that Ct?\u00a0 That’s the small capacitor I highlighted in red.\u00a0 In every game I’ve seen with a 3771 based reset, it’s generally a capacitor in the 10uf range.\u00a0 What this does is cause a small hold delay between when the 3771 sees 4.2v and when it actually releases the reset line, which allows the power supply to come up to voltage properly<\/strong> before the game tries to boot.\u00a0 This matters because without a delay the 3771 is happy to trigger a reset and boot at 4.2v, less than the 5v required for reliable operation of half the logic chips on the PCB.<\/p>\n<\/a><\/p>\n